It is desirable in the operation of an automobile engine to supply combustion supporting air at approximately a predetermined operating temperature, for example at 70.degree. F., during cruise or light acceleration. At ambient temperatures below the desired operating temperature, preheated inlet air and cooler ambient air are supplied to the customary inlet air cleaner in variable proportions via separate ports to obtain the desired operating temperature for the inlet air mixture. The openings for the separate ports for the preheated and ambient air are controlled by a flow control gate operated by a vacuum motor responsive to the temperature modulated pressure of a vacuum source. The U.S. Pat. No. 3,444,847 to King illustrates a conventional inlet air temperature system wherein the vacuum source comprises the inlet manifold pressure modulated by a temperature controlled variable air bleed to the atmosphere. The air bleed is varied in response to the temperature of the inlet air mixture downstream of the flow control gate.
During cruise or steady state operation of the automobile, the temperature modulated vacuum source maintains the vacuum motor and flow control gate at positions required for proper inlet air temperature. Upon rapid acceleration from the cruise condition, the intake manifold vacuum becomes insufficient to hold the vacuum motor and flow control gate at the cruise condition, whereupon the flow control gate opens wide to the ambient inlet air and closes to the pre-heated inlet air. The resulting sudden drop in inlet air temperature often adversely affects engine driveability. When the inlet air mixture is below a predetermined temperature, say about 50.degree. F., the engine is usually operating below its optimum operating temperature. It is then preferable to maintain the flow control gate open to the pre-heated inlet air even during acceleration. Above approximately 50.degree. F., the colder ambient air is desired for improved acceleration, but preferably should be added gradually during the initial acceleration to achieve optimum driveability, particularly with automobile engines operating with lean fuel-air mixtures.
An important object of the present invention is to provide improved means including a temperature controlled check valve between the customary temperature modulated vacuum source and the vacuum motor, such that the vacuum motor is freely connected with the modulated vacuum source at all ambient temperatures when the pressure at the source is less than the pressure at the motor. As the pressure at the modulated vacuum source increases during rapid acceleration when the inlet air mixture downstream of the flow control gate is colder than a predetermined temperature, say 50.degree. F., fluid flow to the motor is positively blocked. Thus, the movement of the vacuum motor and of the flow control gate to increase the proportion of colder inlet air is also blocked. However, the check valve permits such movement at a retarded rate with respect to the change in the modulated vacuum pressure during acceleration when the above defined inlet air mixture is warmer than the predetermined temperature.
In accordance with the foregoing, when the temperature of the inlet air mixture is below 50.degree. F. during cruising conditions, the pressure of the modulated vacuum source operates the vacuum motor to move the flow control gate to a position for supplying pre-heated inlet air tending to raise the temperature of the inlet air mixture to the desired 70.degree. F. operating temperature. During rapid acceleration, the vacuum motor will not respond to a change in the pressure at the vacuum source and the flow control gate will remain open go the pre-heated inlet air.
When the temperature of the inlet air mixture rises above 50.degree. F., the vacuum motor will operate to move the flow control gate gradually to increase the proportion of cooler ambient air in the inlet air mixture during rapid acceleration. Thus, the engine will receive a cooler inlet air mixture as desired for optimum acceleration, but will not stumble momentarily as a result of a sudden drop in inlet air temperature during the initial stage of the acceleration.
Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.